Definition of "tailboard"
A hinged board or hatch at the rear of a vehicle that can be lowered for loading and unloading; a tailgate.
Quotations
She got one knee up under him and hurled him off, and was over the tail-board in a flash, landing on her feet like a cat, and panting hard, by the sudden release of a violent emotion.
1938, Norman Lindsay, Age of Consent, 1st Australian edition, Sydney, N.S.W.: Ure Smith, published 1962, page 171